Data centers, the nondescript warehouses packed with racks of servers that power the modern internet, have been around for decades. But the amount of electricity they need now is soaring because of AI. Training artificial intelligence models and using AI to execute even simple tasks involves ever more complicated, faster and voluminous computations that are straining the electricity system. The data-center-driven resurgence in fossil fuel power contrasts starkly with the sustainability commitments of tech giants Microsoft, Google, Amazon and Meta, all of which say they will erase their emissions entirely as soon as 2030.